As noted our invention relates generally to a method and a means for introducing a medicament into a living organism and in particular to the use of a neutral hydrogel to selectively control the rate at which such medicaments are released within a specified region and/or organ of the body.
In the past, drugs or pharmaceutical preparations have been mixed with carrier agents, such as beeswax, peanut oil, stearates, etc., and injected intramuscularly into the body. The carrier is then slowly broken down within the body allowing a slow release of the drug. Such carriers do not give satisfactory results because they often produce undesirable effects, such as foreign body reaction and scar formation; in addition, granulomas (benign fibrous tumors) and sterile abscesses are formed at the site of the injection. In most cases the rate of release of the therapeutic agent is so rapid that frequent injections become necessary with only small amounts of active agent in each injection. Furthermore, the bulk of the carrier substance limits the amount of active agent that may be used in each injection. A further practical drawback to this form of introducing medication follows from the fact that injections are active for only a few days or a week.
Heretofore, containers of many types have been designed for use within the body cavities whereby medicinal preparations are allowed to escape therefrom. Experience has demonstrated however that such previous attempts have not been fully satisfactory for a variety of reasons including the failure of such containers to adequately control the release of the medicament contained therein. Moreover, elaborate arrangements for depositing medication within the body involving the use of dense tablet forms which have a smooth compacted surface, a portion of which is covered with a protective undissolvable coating have also proved in certain cases to be ineffective. That is, the resorption of the medication from the exposed surface thereof cannot be controlled or predicted during the dissolution of such a tablet.
The problem of controlling the release of a medicament over a prolonged period of time when in contact with a living system has also been approached from a chemical point of view. That is to say, that soluble linear polymers have been utilized as drug carriers wherein the drugs are bound to said polymers by ionic and/or coordination bonds. It is further noted that polymeric salts of basic medicaments have also been employed to prolong the release thereof.
A still further approach to the subject problem has been the implantation of polymeric carriers such as three dimensional hydrophilic polymers which are fully insoluble in body liquids. It has been found that biologically active substances can be absorbed into such polymeric hydrophilic carriers and/or freely deposited any place therein, e.g., in its center, either as solids, dispersions, or as solutions. When exposed to living tissue the active substance diffuses gradually into the surrounding body tissue. The amount of active substance penetrating into the organism in a given time unit can be determined in advance according to the known, measured diffusion rate, the thickness of the polymer layer, the size of the contact surface and the concentration difference. In this connection it is noted that the release of the drug cannot be controlled through a single outlet therefor, but rather diffuses through the entire surface of the surrounding polymeric material.